Its federal biologist caretakers at the U.S. Fish and Wildlife Service's Leadville National Fish Hatchery try to entice the fish by dispensing grated beef liver, fresh shrimp and imported $11-a-pound Otohime morsels from Japan.

Decades of inbreeding also have rendered the greenback cutthroat extra susceptible to sickness. And when humans approach, the trout bangs against the concrete tank walls.

So hatchery manager Ed Stege fills the tanks with purified water and, as much as possible, shields the fish from visitors.

Ed Stege, manager of the Leadville hatchery, says the colder water above 10,000 feet is similar to conditions where the greenback cutthroat trout evolved. (RJ Sangosti, The Denver Post)

"I'm trying to reduce stress on these fish," Stege said. "The happier you can keep them, the lesser the mortality and the better their growth rate."

Such are the tricks in a state-federal breeding blitz to rescue greenback cutthroats from extinction.

Only they carry the genetic print of their ancestors. Faster breeding means federal authorities, when they complete a review, could deem greenback cutthroats "threatened" rather than "endangered."

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For decades, Colorado wildlife officials boosted populations of other cutthroat trout species — in the mistaken belief that those were endangered greenback cutthroat.

Not so, said University of Colorado researcher Jessica Metcalf, an expert in ancient DNA forensics, who located original South Platte River headwaters specimens in museums and analyzed their genes.

The trout are bred in tanks at the hatchery, which dates to the 1880s. (RJ Sangosti, The Denver Post)

This genetic investigation had to be done because pervasive fish-stocking around the Rocky Mountain region, including non-native fish, has scrambled the natural distribution of species. Back in the 19th century, even salmon were dropped into Colorado's high country.

The true greenback cutthroats evolved in chilly headwaters flowing into the South Platte, while Bear Creek flows into the Arkansas River. A U.S. Fish and Wildlife Service fish genealogist discovered that an 1880s hotel promoter, trying to ensure better fishing to lure patrons, transplanted some from the South Platte into Bear Creek where — through mining booms, droughts and development — the species survived.

"We want to preserve biodiversity," Metcalf said. "It's important for healthy ecosystems. This is part of a bigger picture of not ending up in a world of pigeons, cockroaches and brown trout."

Colorado Parks and Wildlife officials have launched simultaneous breeding operations at state hatcheries. And CPW crews recently released 1,200 yearlings from the federal hatchery into Zimmerman Lake, west of Fort Collins, where they can face wild selection pressures instead of hatchery pressures.

A threatened species listing, short of endangered status, would give state wildlife managers greater flexibility and lead to less restriction of fishing at lakes where greenback cutthroats are introduced, said Doug Krieger, senior aquatic biologist for the state.

"We don't have to wait to do the right thing for this fish," he said. "The more places we can get this fish, the more security we can bring."

Krieger was among those who first noticed that cutthroats in Bear Creek looked unusual — before the DNA sleuthing began. "More spots. Smaller spots. Spots on the front of the fish. Some spots on the head," he said.

"These fish are really depleted in their genetics," he said. "It's an in-breeding situation and the end result is that they are compromised in their ability to adapt to changing situations."

Beyond Zimmerman Lake, state officials are mulling reintroductions along Guanella Pass and around the South Platte Basin. They aim to establish 20 stable populations in different rivers and streams, each consisting of 4,000 to 5,000 greenback cutthroats, said Kevin Rogers, a CPW cutthroat trout researcher.

"The challenge is not just in raising the fish, but in making their habitat available for them," Rogers said. "These won't do well with any kind of competition. We have to find places where we can put these fish in and expect them to do well. We have to clear out their habitat of non-native competition so that they can flourish the way they did a hundred years ago."

At the federal hatchery, Stege said the captive population is growing: 530 adults, 1,100 yearlings and more than 3,000 egg and larval-stage fish.

Federal biologists will try to improve them, Stege said. They'll select a robust-looking group, test their genes, and put tiny identity tags on each fish. "Then we can try to cross the most unrelated fish," he said. "We can maximize what limited genetics are out there."

Rockies are on pace to lose 93 games this seasonThe Rockies lost three of four in St. Louis and are on pace to lose 93 games as they come home for a three-game series with Seattle before going back on the road again to face Washington.